that foam ring around the lens; what is it for?

[buckfast]

hey all

In my haste of reassembly of my Dahua 5321Z, have left off the foam ring surrounding the lens inside.

I had it apart to try fix an auto focus issue (which thankfully appears to be rectified) due to a somewhat stupid move of working on the camera body while still powered.

So, of course the foam ring is there for a reason. I just don't know why it is there and the implications of leaving it off. Any thoughts?

thanks

 

[crw030]

Total guess, but I believe it is primarily there to reduce IR bleed thru directly into the camera lens area. Since the IR LEDs are usually assembled in close proximity to the camera lens their natural diffusion would glare right into the lens FoV.

 

[buckfast]

That's seems very plausible

 

[TonyR]

@crw030 is correct, so much so that it led to this Hikvision tech bulletin, attached below:

 

[buckfast]

here's a snapshot from night with IR on, without the foam ring. there is some sort of diagonal spider web like image. i have done a quick search of images for ir reflection and i am not sure that it explains what's in this snapshot